Surface Processes, Weathering, Erosion, and Soils
Domain 5 covers weathering, erosion, mass wasting, streams, groundwater, glaciers, wind, coasts, and soil formation.
Core rules and concepts
- Weathering breaks rock in place; erosion transports sediment. Mechanical weathering includes frost wedging and abrasion; chemical weathering includes hydrolysis, oxidation, and dissolution.
- Soil forms from parent material, climate, organisms, relief, and time. A typical profile is O, A, E, B, C, R; topsoil is A, subsoil is B.
- Streams erode, transport, and deposit sediment; gradient, discharge, channel shape, and base level control behavior. Larger clasts generally settle first.
- Groundwater moves through pores and fractures; porosity is storage, permeability is flow. The water table separates saturated from unsaturated zones.
- Mass wasting is gravity-driven; slope, water, and material strength control it.
- Glaciers erode and deposit till, erratics, and moraines; wind produces dunes and loess.
Worked example
A stream drops from 200 m to 50 m over 5 km. Gradient = (200 − 50) m / 5 km = 150/5 = 30 m/km. A steeper gradient generally increases velocity and erosive power, but discharge and channel roughness also matter. The units are vertical distance per horizontal distance, not degrees.
Traps that cost marks
Weathering is not transport. High porosity does not guarantee high permeability. Soil horizons are not ordered C-A-B-O. Deposition does not sort perfectly by density alone; grain size and current energy matter. A landslide can occur on a gentle slope if water or clay reduces strength.